Polycarbonate (hereinafter may be abbreviated as PC) resins which are formed of an aromatic polycarbonate unit and an aliphatic polyether unit are known to have high toughness. There has been disclosed an exemplary method for producing such a polycarbonate, the method including copolymerizing a phenol-modified diol (diester diol) which has been derived from p-hydroxybenzoic acid, an alkyl ester thereof, or an acid chloride thereof, and a diol (see, for example, Patent Document 1). Specifically, PC copolymers produced through copolymerization of tetramethylene glycol (molecular weight: 2,000)-bis(4-hydroxybenzoate) or polyethylene glycol (molecular weight: 8,000)-bis(4-hydroxybenzoate) have been proposed. These PC copolymers formed from a diester diol can be produced through a conventional interfacial polymerization method. However, during a step of washing polymerization liquid, the methylene chloride phase containing a PC copolymer and the aqueous phase containing impurities are difficult to separate from each other. Thus, high-purity PC copolymers fail to be obtained, or high-purity PC copolymers are produced merely at considerably low productivity, which is problematic.
Although PC resin is widely employed as a transparent resin having high impact strength, there is continuous demand for improvement in other properties of PC resin. One known approach for improvement is copolymerization of a compound having a structure other than bisphenol A (e.g., introduction of aliphatic chain), whereby flowability of the resin is enhanced.
In the production method disclosed in Patent Document 1, poly(alkylene ether glycol)-bis(hydroxybenzoate ester) is employed as a phenol-modified diol. Before use, the poly(alkylene ether glycol)-bis(hydroxybenzoate ester) is not subjected to purification.
In addition to production of PC resin, use of poly(alkylene ether glycol)-bis(hydroxybenzoate ester) has been proposed for producing polyurethane and epoxy resin, and a synthesis method thereof is disclosed (see, for example, Patent Document 2 or 3). However, the Patent Documents do not disclose purification of the phenol-modified diol.
PC resin can be produced through a method such as interfacial polymerization or melt polymerization. In the case where PC copolymer is produced through interfacial polymerization of poly(alkylene ether glycol)-bis(hydroxybenzoate ester) serving as a starting material, separation of the aqueous phase from the organic phase performed in the washing step takes a long time or becomes difficult, which is problematic.
[Patent Document 1]
    Japanese Patent Application Laid-Open (kokai) No. 62-79222[Patent Document 2]    Japanese Patent Application Laid-Open (kokai) No. 60-79072[Patent Document 3]    Japanese Patent Application Laid-Open (kokai) No. 2002-173465